A study was conducted to evaluate the nephrotoxic effect of ochratoxin A (OTA) in broiler chickens. Forty Ross 308 broilers (6 days old) were divided into two groups: one group received daily, by gavage, ochratoxin A at a daily dose of 50 μg/kg body weight for up to 21 days, while the control group received only diluent (sunflower oil). After 21 days, the chickens were euthanised and the kidneys removed for analysis by histopathology and immunohistochemistry to detect an anti-apoptotic marker (Bcl-2), and by transmission electron microscopy. Macroscopically the kidneys were enlarged, showing degeneration and gout deposits. Histologically, glomerulonephrosis and tubulonephrosis were common lesions in all chicks. In two of the five chicks exposed to OTA for 21 days, focal tubular cell proliferation, multiple adenoma-like structures and Bcl-2-positive epithelial cells were identified in layers of the renal papilla and in convoluted tubules. Transmission electron microscopy of the proximal convoluted tubules identified abnormal forms of mitochondria. The nephrotoxic effect of ochratoxicosis in chickens is probably due to carcinogenic changes induced in the epithelial tissues.